Olanzapine has shown great promise in the treatment of patients suffering from schizophrenia and is currently being marketed for that purpose. However, such patients are often non-compliant, making it difficult to assess whether or not a patient has received the proper dosage of medication. It is therefore desirable to formulate olanzapine in a sustained release or depot formulation to assure consistent and proper dosage of the drug substance and to assume compliance. U.S. Pat. No. 6,169,084 B1 discloses certain olanzapine pamoate salts and solvates thereof, such as the olanzapine pamoate monohydrate, which are useful in preparing such sustained release or depot formulations.
In order to achieve a sustained release formulation of 2 to 4 weeks, for example, an injectable, slow to dissolve form of the active compound is needed. Surprisingly, olanzapine pamoate can be prepared in the dihydrate form. In addition, olanzapine pamoate dihydrate is substantially less soluble in aqueous solution than olanzapine pamoate monohydrate. Thus, the olanzapine pamoate dihydrate has excellent properties for use as a depot preparation.